Opioid peptides (i.e. enkephalins and endorphins) affect immune system functions (e.g. antibody production, cell proliferation, cytotoxicity, lymphokine production, and chemotaxis). In addition to being targets of opioid modulation, specific immunocompetent cell types are also a source of opioid peptides. These data have led to the suggestion that opioid peptides serve as regulatory signals between the neuroendocrine and immune systems as well as among immune system cells. Preliminary studies of opioid modulation of severely compromised immune systems (e.g. acquired immunodeficiency syndrome and cancer) are already being reported. Extracellularly oriented cell surface peptidases (ectopeptidases) play a key role in metabolism and inactivation of opioid peptides in several tissues. We postulate that ectopeptidases are also important in the immune system in modulating local opioid concentrations and the spectrum of inactive and active opioid peptides produced. Particular cell surface antigens used to characterize hemopoietic cells have recently been identified as ectopeptidases (e.g. CALLA/CD10 as neutral endopeptidase and CD13 as aminopeptidase N). In addition, inhibitors of ectopeptidase activity affect proliferation and differentiation of B cells and activation of T cells. Our broad goal is to better understand the regulatory role of ectopeptidases in the physiological response of immunocompetent cells to opioid peptides. Our first specific aim is to identify and characterize the ectopeptidases metabolizing enkephalins in immunocompetent cells, using HPLC to identify opioid peptide products, and to identify the cell subtypes expressing these activities. In the second specific aim, the regulation of the expression of these ectopeptidases and in response to specific stimuli will be investigated using assays of ectopeptidase activity, enzyme protein, and mRNA levels. The third specific aim is to investigate the importance of these ectopeptidases in modulation of tbe responses of immunocompetent cell function to opioid peptides. Enkephalin inhibition of immobilized anti-CD3 stimulated T cell proliferation is a simple functional assay that will be initially used to investigate this question. Successful completion of these studies will provide a solid biochemical foundation for future therapeutic approaches to immune system dysfunctions.